It is generally known that organosilicon compounds containing substituted carbamoyloxy groups (.tbd.SiOCO--NH--) which are bonded to silicon via oxygen can be prepared by reacting organosilanols with isocyanates. Also, British Pat. No. 888,938 suggests that polysiloxanes containing Si-bonded hydroxyl groups can be reacted with bivalent or trivalent isocyanates. However, when the polysiloxanes contain SiC-bonded organic radicals instead of alkoxypolysiloxanes, such as di-tert-butoxypolysiloxanes, the reacton with the isocyanates does not produce organopolysiloxanes containing carbamoyloxy groups. Often no reaction will take place, or when a reaction does occur, only water is split off from the Si-bonded hydroxyl groups of the organopolysiloxanes, thereby resulting in an increase in the viscosity of the organopolysiloxanes. In contrast to the teachings of the British patent, the process of this invention results in the formation of organopolysiloxanes having substituted carbamoyloxy groups bonded to silicon atoms via oxygen.
Adhesive repellent coatings are described in Canadian Pat. No. 832,520 and British Pat. No. 1,342,229 in which an organopolysiloxane having Si-bonded hydroxyl groups is mixed with an organic isocyanate, an organic tin compound, a silicic acid ester and an organopolysiloxane containing Si-bonded hydrogen or an acetoxysilane. These patents do not, however, disclose reacting an organopolysiloxane having hydroxyl groups with an organic isocyanate as the sole reactants in the presence of an organic tin compound to form an organopolysiloxane having substituted carbamoyloxy groups bonded to silicon via oxygen. Likewise, these patents are devoid of any suggestion that the compositions or coatings contain substituted carbamoyloxy groups which are bonded to the silicon atoms of the organopolysiloxane via oxygen atoms.
Therefore, it is an object of this invention to provide organopolysiloxanes having substituted carbamoyloxy groups bonded to the silicon atoms via oxygen. Another object of this invention is to provide organopolysiloxanes having substituted carbamoyloxy groups bonded to the silicon atoms via oxygen which have improved stability. A further object of this invention is to provide a process for preparing organopolysiloxanes having substituted carbamoyloxy groups bonded to silicon atoms via oxygen. A still further object of this invention is to provide a process for improving the stability of organopolysiloxanes having substituted carbamoyloxy groups bonded to silicon atoms via oxygen.